British Journal of Radiology 75 (2002),627-634 © 2002 The British Institute of Radiology
MRI of the sternum and sternoclavicular joints
M Aslam, FRCR,
A Rajesh, FRCR,
J Entwisle, MRCP, FRCR and
K Jeyapalan, MRCP, FRCR
Glenfield Hospital NHS Trust, Leicester LE3 9QP, UK
Correspondence: Dr Mohammad Aslam, FRCR, Consultant Radiologist, Southend Hospital, Prittle Well Chase, Westcliff on Sea, Essex SS0 0RY, UK
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Abstract
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The sternum and sternoclavicular joints are difficult to evaluate with plain radiographs. The value of CT in assessing lesions of the sternum and sternoclavicular joints has been well documented, but the potential role of MRI has not been emphasized. We present the MRI techniques, normal appearances and a spectrum of abnormalities, and emphasize the role of MRI as a useful radiological investigation for the sternum and sternoclavicular joints.
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Introduction
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MRI is ideal for imaging the sternum because of its multiplanar capability as well as excellent spatial and contrast resolution. It characterizes cartilage and soft tissue better than CT, and is also more sensitive to marrow oedema and replacement.
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Technique
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Breath-hold images were obtained in three orthogonal planes, coronal, sagittal and axial, using a general purpose body array coil on a 1.5 T Siemens Vision scanner (Siemens, Erlangen, Germany). Coronal images were obtained in two oblique planes, one parallel to the manubrium and the other parallel to the body of the sternum. Both T1 and T2 weighted images were acquired. Short tau inversion recovery (STIR) or fat suppressed T2 weighted images were acquired in the optimal plane to depict the pathology. Respiratory gating was required for STIR sequences only.
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Normal appearances
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The sternum is optimally demonstrated in the sagittal plane with clear delineation of the manubrium, the body of the sternum and the xiphoid process. The outer cortex and central marrow are well seen (Figure 1
). Coronal images are obtained in two planes for clear views of the manubrium and body of the sternum as they are angulated at the manubriosternal junction. The axial images provide additional information, particularly in the evaluation of congenital chest wall deformities.
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Figure 1. (a) Coronal and (b) sagittal T2 weighted images and (c) sagittal T1 weighted image of the normal sternum. The manubrium, body and xiphoid process are clearly visualized. The coronal image is in a plane parallel to the body of the sternum. (d) Coronal T2 image in a plane parallel to the manubrium depicting the sternoclavicular joints (SCJs). On the coronal oblique images, the costochondral and chondrosternal junctions are well seen (a,d). The SCJs with the articular surfaces, covering fibrocartilage and articular disc are well depicted (d,e).
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Although uncommon, a wide spectrum of pathological processes may involve the sternum. These include congenital abnormalities such as pectus excavatum, Poland's syndrome, infections, trauma, sternotomy complications and tumours.
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Congenital disorders
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Pectus excavatum
Pectus excavatum is the most common congenital deformity of the sternum, resulting in reduction of prevertebral space, leftward displacement and axial rotation of the heart as well as reduction in the space occupied by the left lung. MRI is useful in the demonstration of anatomy in patients with severe pectus who need corrective surgery. Sagittal MR images depict the depressed sternum in its entire length, while the axial images clearly demonstrate the reduction in the midline anteroposterior diameter (Figure 2). The severity of the deformity can be quantified using the pectus index, derived by dividing the transverse diameter of the chest by the anteroposterior diameter, obtained on axial MR images. A pectus index greater than 3.25 necessitates surgical correction [1, 2]. Sternal deformity due to unfused segments in young patients is also well depicted (Figure 3).
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Figure 2. Severe pectus excavatum. (a) Axial and (b) sagittal T1 weighted images showing sternal depression with decrease in the anteroposterior diameter of the thorax and deviation of the heart. Deformity of the sternal body and xiphoid process are seen well on the coronal slices. (c) Axial T1 weighted image of minor pectus excavatum. Goretex sheet used for pectoplasty is visible on the left side (arrowhead).
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Figure 3. Unfused segments of the body of the sternum with angulation of the sternum in an 18-year-old male. The sternal segments usually fuse around puberty.
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Poland's syndrome
Poland's syndrome is an uncommon congenital aberration of the chest wall characterized by partial or total absence of the pectoralis major muscle and syndactyly [3]. Other associated chest wall abnormalities include absence or atrophy of the second to fifth ipsilateral ribs, and other chest wall muscles. MRI depicts the absence of the greater pectoral muscle and also clearly shows the associated costal cartilage, rib and muscle deficiencies (Figure 4).
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Figure 4. Poland's syndrome. (a) Coronal T2 weighted, (b) axial T1 weighted and (c) coronal T1 weighted images showing absence of the pectoralis major and minor muscles, serratus anterior and lattisimus dorsi on the right side. The rhomboids are hypoplastic as well. Coronal sections show the absence of the sternal and clavicular heads of the pectoralis muscles on the right side and deformity of the sternum.
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Trauma
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Sternal fractures constitute 5–10% of all thoracic injuries [4] and usually occur as a result of direct trauma from steering wheel or seat belt injuries. Fractures of the sternum can be difficult to evaluate on plain radiographs due to overlying soft tissue or technical reasons. Although sagittal MRI can delineate fractures clearly, assessment of bony union can be very difficult until the union is very mature (Figure 5). Patients with sternal injuries often have associated injuries of the mediastum and spine, which can also be evaluated with MRI.
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Figure 5. Sagittal (a) T1 and (b) T2 weighted images of the sternum depict a healed fracture. Site of bone healing and the resulting deformity are demonstrated.
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Degenerative disease
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Degenerative disease of the sternoclavicular joints (SCJs) is best seen on oblique coronal images. Narrowing of joint space, capsular hypertrophy and osteophyte formation is well demonstrated on MRI (Figure 6). CT can also demonstrate these findings, although this involves radiation.
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Figure 6. Oblique coronal T2 weighted image shows narrowing of the sternoclavicular joint space inferiorly, capsular hypertrophy and marginal osteophyte on the left side in a patient with osteoarthritis.
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Osteitis condensans of the clavicle
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Osteitis condensans of the clavicle is thought to be a response to mechanical stress, and not a complication of pregnancy. MRI shows sclerosis and enlargement of the medial end of the clavicle. The joint space is usually preserved (Figure 7).
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Figure 7. Oblique coronal T1 weighted images showing low signal in the medial end of the right clavicle, suggesting sclerosis in a patient with osteitis condensans.
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Infections
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Primary infection of the sternum is rare but can occur spontaneously or secondary to diabetes, immunosuppresion or trauma (Figure 8). Staphylococcus aureus and Pseudomonas aeruginosa are the most common causative organisms of pyogenic infections [5]. Tuberculosis of the sternum, although rare, is increasing in incidence owing to the increasing number of HIV infected patients (Figure 9). Pyogenic infections and tuberculosis of the sternum are associated with destruction of bone, marrow infiltration, periosteal elevation and a soft tissue component. MRI is useful for determining the extent of the lesion, particularly marrow involvement and soft tissue spread. Abscess formation, destruction of articular cartilage and sinus tract formation is particularly well depicted by MRI. These findings are not visualized on radiography until destruction is advanced [4, 6]. The recognition of post-sternotomy complications, such as sternal dehiscence and osteomyelitis, are crucial as the overall mortality rate from these complications exceeds 50% (Figure 10) [7]. MRI, although useful, has some limitations due to artefacts from sternal wires.
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Figure 8. Osteomyelitis of the sternum. Sagittal (a) T2 weighted and (b) T1 weighted images showing a collection around the sternum, destruction of the distal half of the manubrium and adjacent body of the sternum, and soft tissue swelling in the pre- and retro-sternal areas. Extensive anterior periosteal elevation with sub-periosteal collection is also noted.
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Figure 9. Tuberculosis. Short tau inversion recovery (STIR) sagittal image showing destruction on the middle third of the sternum with a collection around it. The collection is high signal on STIR.
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Figure 10. Axial (a) T1 and (b) T2 weighted images showing a collection around the sternum on the right side with a sinus tract extending to the skin in a patient with an infected mesh.
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Tumours
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Chondrosarcomas are the most common malignant tumours of the sternum. Bronchogenic and breast carcinomas are the most common primaries associated with sternal metastases [8]. Plasmacytoma and lymphoma may also involve the sternum (Figure 11). MRI and CT have complementary roles in the evaluation of sternal tumours. CT is useful for identifying the typical cartilaginous matrix of chondrosarcoma. MRI is the technique of choice for evaluating the extent of extraosseous tumour and its relationship to adjacent structures with regard to operability [9].
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Figure 11. Lymphoma. (a) Axial and (b) coronal short tau inversion recovery images show a high signal destructive mass in the manubrium sternum.
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Conclusion
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The sternum and SCJs are ideally imaged by MRI. The sagittal plane is especially useful in evaluating the sternum and retrosternal region. In congenital chest wall deformities such as pectus, secondary effects on intrathoracic structures including the heart are well demonstrated. The extent of bone destruction, marrow infiltration, periosteal elevation and soft tissue component are well delineated in infections as well as primary and secondary tumours. The anatomy and pathology of SCJs is well seen in the coronal oblique plane. Although some centres use prone position and smaller surface coils, we obtained excellent images in the supine position with the body coil [10]. MRI can be a useful investigation for evaluation of the sternum and SCJs, although in some instances other modalities of imaging may be used as an adjunct to diagnoses.
Received for publication March 30, 2001.
Revision received September 3, 2001.
Accepted for publication September 18, 2002.
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Abstract
Introduction
